The present invention relates to devices for improving the quality of data signals and, more particularly, to devices for improving the quality of data signals distorted during transmission over a link.
In data communication networks, network nodes communicate by transmitting analog signals over links, such as a Category-5 cable. The receiving node is responsible for recovering digital data bits from the analog signal. Because distortion is introduced during transmission over the link, the receiving node must generally improve the quality of the signal prior to attempting data recovery. Signal quality is typically improved through a process known as equalization which, generally speaking, compensates for distortion introduced on a link and reshapes the signal closer to its original waveform. Without adequate equalization, distortion might cause either a total inability to recover the transmitted data, or recovery of data with an unacceptably high incidence of bit errors.
Equalization presents technical challenges because the nature and extent of distortion varies from network-to-network and link-to-link. The nature of distortion may be affected by numerous factors, such as channel length, transmission frequency, impedance mismatch, electromagnetic interference, and, to a generally lesser extent, impediments in connectors and coupling transformers, manufacturing variations and environmental factors such as temperature. Additional complications may arise from the dependence of some distortion-causing variables on others, such as the frequency dependency of signal attenuation for a given channel length.
Due to the often complex mix of factors causing distortion on real-world links, adaptive equalization has generally been favored over static equalization to compensate for such distortion. Static equalization applies a fixed corrective response, or xe2x80x9ctapxe2x80x9d, to a signal. Static equalization is therefore not well suited to compensating for distortion that is unpredictable and time-variant. Conventional adaptive equalization, on the other hand, applies a dynamic corrective response to a signal, which response is updated in real-time based on continuous sampling of the signal, and is therefore better able to compensate for unpredictable and time-dependent distortion. Better signal quality and lower bit error rates result.
However, conventional adaptive equalization is not without its shortcomings. Conventional adaptive equalization has generally required substantial overhead, i.e. large gate count, which has translated into high chip costs. For links where distortion is relatively predictable and varies slowly with time, such adaptive equalization may therefore be xe2x80x9coverkillxe2x80x9d. It has been found, for instance, that distortion introduced on multichannel Gigabit Ethernet links over Category-5 cable is primarily caused by impedence mismatch producing reflections within a channel and crosstalk between the channels, and does not change very rapidly. For such multichannel links, a receiving node implementing a novel equalization that leverages shared equalization resources to improve the quality of multiple signals, and updates the corrective responses applied to such signals only when necessary (i.e. not in real-time), may achieve acceptable bit error rates with far less overhead than would be required by conventional adaptive equalization.
In a basic feature, the present invention provides a novel equalization apparatus and method therefor for improving the quality of signals received over a multichannel link. The method generates dedicated tap coefficients for a plurality of input signals received over the link including sampling the input signals and applying the samples in a shared tap coefficient algorithm, which tap coefficients are applied to the input signals to which they are dedicated to generate output signals and are updated based upon degradation in the quality of the output signals corresponding to the input signals to which the tap coefficients are applied. Degradation in the quality of output signals is measured by comparing the bit error rate of the output signals with a predetermined threshold.
The apparatus includes an equalization controller shared among a plurality of input signals and arranged to generate a dedicated tap coefficient for each input signal including sampling the input signal in a first instance and applying the first sample as an input to a tap coefficient algorithm, and arranged to update the dedicated tap coefficient for the input signal including sampling the input signal in a second instance in accordance with feedback received by a performance monitor and applying the second sample as an input to the tap coefficient algorithm.
The apparatus further includes a signal filter dedicated to each input signal and arranged to generate an output signal including receiving the input signal and applying the input signal as a first input to a plurality of multiply functions, each multiply function having as a second input a different coefficient within a dedicated coefficient set received from the equalization controller to generate a plurality of products, and applying the plurality of products to an accumulate function.
The apparatus further includes a performance monitor dedicated to each output signal and arranged to apply feedback to an equalization controller including comparing the bit error rate of the output signal with a predetermined threshold and generating a feedback signal upon the output signal exceeding a predetermined threshold.